A New Cyberinfrastructure for the Natural Hazards Community

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1 A New Cyberinfrastructure for the Natural Hazards Community 1

2 Agenda Introduction to the Jupyter Notebook Programming in Python Plotting with Matplotlib Putting everything together a scientific notebook from Scott J. Brandenberg, Ph.D., P.E. Associate Professor Department of Civil and Environmental Engineering University of California 2

3 What are Jupyter Notebooks? A web-based, interactive computing tool for capturing the whole computation process: developing, documenting, and executing code, as well as communicating the results. 3

4 How do Jupyter Notebooks Work? An open notebook has exactly one interactive session connected to a kernel which will execute code sent by the user and communicate back results. This kernel remains active if the web browser window is closed, and reopening the same notebook from the dashboard will reconnect the web application to the same kernel. What's this mean? Notebooks are an interface to kernel, the kernel executes your code and outputs back to you through the notebook. The kernel is essentially our programming language we wish to interface with. 4

5 Jupyter Notebooks, Structure Code Cells Code cells allow you to enter and run code Run a code cell using Shift-Enter Markdown Cells Text can be added to Jupyter Notebooks using Markdown cells. Markdown is a popular markup language that is a superset of HTML. 5

6 Jupyter Notebooks, Structure Markdown Cells You can add headings: # Heading 1 # Heading 2 ## Heading 2.1 ## Heading 2.2 You can add lists 1. First ordered list item 2. Another item * Unordered sub-list. 1. Actual numbers don't matter, just that it's a number 1. Ordered sub-list 4. And another item. 6

7 Jupyter Notebooks, Structure Markdown Cells pure HTML <dl> <dt>definition list</dt> <dd>is something people use sometimes.</dd> <dt>markdown in HTML</dt> <dd>does *not* work **very** well. Use HTML <em>tags</em>.</dd> </dl> And even, Latex! $e^{i\pi} + 1 = 0$ 7

8 Jupyter Notebooks, Workflow Typically, you will work on a computational problem in pieces, organizing related ideas into cells and moving forward once previous parts work correctly. This is much more convenient for interactive exploration than breaking up a computation into scripts that must be executed together, as was previously necessary, especially if parts of them take a long time to run. 8

9 Jupyter Notebooks, Workflow Let a traditional paper lab notebook be your guide: Each notebook keeps a historical (and dated) record of the analysis as it s being explored. The notebook is not meant to be anything other than a place for experimentation and development. Notebooks can be split when they get too long. Notebooks can be split by topic, if it makes sense. 9

10 Jupyter Notebooks, Shortcuts Shift-Enter: run cell Execute the current cell, show output (if any), and jump to the next cell below. If Shift-Enteris invoked on the last cell, a new code cell will also be created. Note that in the notebook, typing Enter on its own never forces execution, but rather just inserts a new line in the current cell. Shift-Enter is equivalent to clicking the Cell Run menu item. 10

11 Jupyter Notebooks, Shortcuts Ctrl-Enter: run cell in-place Execute the current cell as if it were in terminal mode, where any output is shown, but the cursor remains in the current cell. The cell s entire contents are selected after execution, so you can just start typing and only the new input will be in the cell. This is convenient for doing quick experiments in place, or for querying things like filesystem content, without needing to create additional cells that you may not want to be saved in the notebook. 11

12 Jupyter Notebooks, Shortcuts Alt-Enter: run cell, insert below Executes the current cell, shows the output, and inserts a new cell between the current cell and the cell below (if one exists). (shortcut for the sequence Shift-Enter,Ctrl-m a. (Ctrl-m a adds a new cell above the current one.)) Esc and Enter: Command mode and edit mode In command mode, you can easily navigate around the notebook using keyboard shortcuts. In edit mode, you can edit text in cells. 12

13 Introduction to Python Hello World! Data types Variables Arithmetic operations Relational operations Input/Output Control Flow More Data Types! Matplotlib the magic number is: 4 13

14 Python print Hello World! Let's type that line of code into a Code Cell, and hit Shift-Enter: Hello World! 14

15 Python print 5 print 1+1 Let's add the above into another Code Cell, and hit Shift-Enter

16 Python - Variables You will need to store data into variables You can use those variables later on You can perform operations with those variables Variables are declared with a name, followed by = and a value An integer, string, When declaring a variable, capitalization is important: A <> a 16

17 Python - Variables in a code cell: five = 5 one = 1 print five print one + one message = This is a string print message Notice: We're not "typing" our variables, we're just setting them and allowing Python to type them for us. 17

18 Python - Data Types in a code cell: integer_variable = 100 floating_point_variable = string_variable = Name Notice: We're not "typing" our variables, we're just setting them and allowing Python to type them for us. 18

19 Python - Data Types Variables have a type You can check the type of a variable by using the type() function: print type(integer_variable) It is also possible to change the type of some basic types: str(int/float): converts an integer/float to a string int(str): converts a string to an integer float(str): converts a string to a float Be careful: you can only convert data that actually makes sense to be transformed 19

20 Python - Arithmetic Operations + Addition = 2 - Subtraction 5 3 = 2 / Division 4 / 2 = 2 % Modulo 5 % 2 = 1 * Multiplication 5 * 2 = 10 // Floor division 5 // 2 = 2 ** To the power of 2 ** 3 = 8 20

21 Python - Arithmetic Operations Some experiments: print 5/2 print 5.0/2 print "hello" + "world" print "some" + 1 print "number" * 5 print 3+5*2 21

22 Python - Reading from the Keyboard Let put the following into a new Code Cell: var = input("please enter a number: ") Let's run this cell! 22

23 Python - Reading from the Keyboard Let put the following into a new Code Cell: var2 = input("please enter a string: ") Let's run this cell! put the word Hello as your input. What happened? 23

24 Python - Making the output prettier Let put the following into a new Code Cell: print "The number that you wrote was : ", var print "The number that you wrote was : %d" % var print "the string you entered was: ", var2 print "the string you entered was: %s" % var2 Want to make it prettier? \n for a new line \t to insert a tab for floating points, us %f 24

25 Python - Writing to a File Let put the following into a new Code Cell: my_file = open("output_file.txt",'w') vars = "This is a string\n" my_file.write(vars) var3 = 10 my_file.write("\n") my_file.write(str(var3)) var4 = 20.0 my_file.write("\n") my_file.write(str(var4)) my_file.close() for floating points, us %f 25

26 Python - Reading from a File When opening a file, you need to decide how you want to open it: Just read? Are you going to write to the file? If the file already exists, what do you want to do with it? r w a read only (default) write mode: file will be overwritten if it already exists append mode: data will be appended to the existing file 26

27 Python - Reading from a File Let's read from the file we created in the previous cell. my_file = open( output_file.txt, r ) content = my_file.read() print content my_file.close() 27

28 Python - Reading from a File Let's read it line by line my_file = open("output_file.txt",'r') vars = my_file.readline() var5 = my_file.readline() var6 = my_file.readline() print "String: ", vars print "Integer: ", var1 print "Float: ", var2 my_file.close() 28

29 Python - Reading from a File Tweak it a bit to make the code easier to read introducing 'with'! (remember the MAGIC NUMBER! Hint: it's 4) with open("output_file.txt",'r') as f: vars = f.readline() var5 = f.readline() var6 = f.readline() print "String: ", vars print "Integer: ", var1 print "Float: ", var2 29

30 Python - Control Flow So far we have been writing instruction after instruction Every instruction is executed What happens if we want to have instructions that are only executed if a given condition is true? 30

31 Python - if/else/elif The if/else construction allows you to define conditions in your program (remember the MAGIC NUMBER! Hint: it's 4) if conditiona: statementa elif conditionb: statementb else: statementd this line will always be executed (after the if/else) 31

32 Python - if/else/elif A simple example if var>10: print "You entered a number greater than 10" else print "you entered a number less than 10" 32

33 Python - if/else/elif The if/else construction allows you to define conditions in your program (remember the MAGIC NUMBER! Hint: it's 4) if condition1: statement1 if condition2: statement2 else: if condition3: statement3 # when is this statement executed? else: # which if does this else belong to? statement4 # when is this statement executed? 33

34 Python - For Loops When we need to iterate, execute the same set of instructions over and over again we need to loop! and introducing range() (remember the MAGIC NUMBER! Hint: it's 4) for x in range(0, 3): print "Let's go %d" % (x) 34

35 Python - While Loops Sometimes we need to loop while a condition is true... (remember the MAGIC NUMBER! Hint: it's 4) i = 0 # Initialization while (i < 10): # Condition print i # do_something i = i + 1 # Why do we need this? 35

36 Python - lists A list is a sequence, where each element is assigned a position (index) First position is 0. You can access each position using [] Elements in the list can be of different type mylist1 = [ first item, second item ] mylist2 = [1, 2, 3, 4] mylist3 = [ first, second, 3] print mylist1[0], mylist1[1] print mylist2[0] print mylist3 print mylist3[0], mylist3[1], mylist3[2] print mylist2[0] + mylist3[2] 36

37 Python - lists It s possible to use slicing: print mylist3[0:3] print mylist3 To change the value of an element in a list, simply assign it a new value: mylist3[0] = 10 print mylist3 37

38 Python - lists There s a function that returns the number of elements in a list len(mylist2) Check if a value exists in a list: 1 in mylist2 Delete an element len(mylist2) del mylist2[0] print mylist2 Iterate over the elements of a list: for x in mylist2: print x 38

39 Python - lists There are more functions max(mylist), min(mylist) It s possible to add new elements to a list: my_list.append(new_item) We know how to find if an element exists, but there s a way to return the position of that element: my_list.index(item) Or how many times a given item appears in the list: my_list.count(item) 39

40 Matplotlib, What is it? It s a graphing library for Python. It has a nice collection of tools that you can use to create anything from simple graphs, to scatter plots, to 3D graphs. It is used heavily in the scientific Python community for data visualisation. 40

41 Matplotlib, First Steps Let's plot a simple sin wave from 0 to 2 pi. First lets, get our code started by importing the necessary modules. %matplotlib inline import matplotlib.pyplot as plt import numpy as np 41

42 Matplotlib, First Steps Let's add the following lines, we're setting up x as an array of 50 elements going from 0 to 2*pi x = np.linspace(0, 2 * np.pi, 50) plt.plot(x, np.sin(x)) plt.show() # Show the graph. Let's run our cell! 42

43 Matplotlib, a bit more interesting Let's plot another curve on the axis plt.plot(x, np.sin(x), x, np.sin(2 * x)) plt.show() Let's run our cell! 43

44 Matplotlib, a bit more interesting Let's see if we can make the plots easier to read plt.plot(x, np.sin(x), 'r-o', x, np.cos(x), 'g--') plt.show() Let's run this cell! 44

45 Matplotlib, a bit more interesting Colors: Blue b Green g Red r Cyan c Magenta m Yellow y Black k ( b is taken by blue so the last letter is used) White w 45

46 Matplotlib, a bit more interesting Lines: Solid Line - Dashed Dotted. Dash-dotted -: Often Used Markers: Point. Pixel, Circle o Square s Triangle ^ 46

47 Matplotlib, Subplots Let's split the plots up into subplots plt.subplot(2, 1, 1) # (row, column, active area) plt.plot(x, np.sin(x), 'r') plt.subplot(2, 1, 2) plt.plot(x, np.cos(x), 'g') plt.show() using the subplot() function, we can plot two graphs at the same time within the same "canvas". Think of the subplots as "tables", each subplot is set with the number of rows, the number of columns, and the active area, the active areas are numbered left to right, then up to down. 47

48 Matplotlib, Scatter Plots Let's take our sin curve, and make it a scatter plot y = np.sin(x) plt.scatter(x,y) plt.show() call the scatter() function and pass it two arrays of x and y coordinates. 48

49 Matplotlib, add a touch of color Let's mix things up, using random numbers and add a colormap to a scatter plot x = np.random.rand(1000) y = np.random.rand(1000) size = np.random.rand(1000) * 50 color = np.random.rand(1000) plt.scatter(x, y, size, color) plt.colorbar() plt.show() 49

50 Matplotlib, add a touch of color Let's see what we added, and where that takes us... plt.scatter(x, y, size, color) plt.colorbar()... We brought in two new parameters, size and color. Which will varies the diameter and the color of our points. Then adding the colorbar() gives us nice color legend to the side. 50

51 Matplotlib, Histograms A histogram is one of the simplest types of graphs to plot in Matplotlib. All you need to do is pass the hist() function an array of data. The second argument specifies the amount of bins to use. Bins are intervals of values that our data will fall into. The more bins, the more bars. plt.hist(x, 50) plt.show() 51

52 Matplotlib, Contour Plots Let's play with our preloaded data. import matplotlib.cm as cm with open('../mydata/contourdata/contourdata.dat') as file: array2d = [[float(digit) for digit in line.split()] for line in file] print array2d nx, ny = np.shape(array2d) cs = plt.pcolor(array2d, cmap=cm.get_cmap('afmhot')) cb = plt.colorbar(cs, orientation = 'horizontal') plt.xlim(0,nx) plt.ylim(0,ny) plt.show() 52

53 Matplotlib, Adding Labels and Legends Let's go back to our sin/cos curve example, and add a bit of clarification to our plots x = np.linspace(0, 2 * np.pi, 50) plt.plot(x, np.sin(x), 'r-x', label='sin(x)') plt.plot(x, np.cos(x), 'g-^', label='cos(x)') plt.legend() # Display the legend. plt.xlabel('rads') # Add a label to the x-axis. plt.ylabel('amplitude') # Add a label to the y-axis. plt.title('sin and Cos Waves') # Add a graph title. plt.show() 53

54 DesignSafe: Questions? For additional questions, feel free to contact us or fill out a ticket: 54

55 An example. presented by: Scott J. Brandenberg, Ph.D., P.E. Associate Professor Department of Civil and Environmental Engineering University of California 55

56 DesignSafe: Thanks Ellen Rathje, Tim Cockerill, Jamie Padgett, Scott Brandenberg, Dan Stanzione, Steve Mock, Matt Hanlon, Josue Coronel, Manuel Rojas, Joe Stubbs, Matt Stelmaszek, Hedda Prochaska, Joonyee Chuah 56

57 DesignSafe: References tml

58 DesignSafe: Next Webinar DesignSafe: Data Analysis and Plotting using Jupyter and R Wednesday, November 9 th 1:00p 3:00p For additional questions, feel free to contact us training@designsafe-ci.org or fill out a ticket: 58

Plotting With matplotlib

Lab Plotting With matplotlib and Mayavi Lab Objective: Introduce some of the basic plotting functions available in matplotlib and Mayavi. -D plotting with matplotlib The Python library matplotlib will